Ceramic capacitor voltage?

[maurycy]

I need to replace few ceramic capacitors on the power amp board. They have markings like "0.1uF KCK" (see picture). What's the voltage I should pick for the replacement cap? Checking Mouser.com website it looks like 0.1uF is listed from 50V to 2KV. Service manual for the amp just lists the capacitance value and not voltage for the ceramic capacitors.

Thanks.

 

[firechief]

Do you have the schematic in digital form? If you post it, we could be sure. Or measure the voltage on both sides of the cap. Also google returns some good hints. When in doubt a higher voltage rating is not a problem. Tube or solid state? Model?

 

[maurycy]

Thanks for replying. The capacitors are on the power amp board in Luxman L-85V solid state amplifier. The boards are shot so I am doing a full rebuild. That's why I can't measure the voltages.

Here is a link to the power amp section: PB-1037

Full schematic can be found here: full schematic

 

[firechief]

OK I see an electrolydic in that power section that is rated at 100V so you would be safe with something like 250V but check the physical size. As the voltage goes up so does the size.

 

[maurycy]

Great. I will check the sizes when ordering replacement caps. Difference in price between 50V and 250V is not that big. Well, actually it is about 3x more but we are talking cents here and I only need maybe 10 of those capacitors.

Thanks for your help.

 

[lucpes]

I have a chinese DAC (X22) that has 8 ceramic capacitors that I'm looking to replace with silvered mica. Micas will be 500V (can not get any lower voltage) so I'd be safe. The capacitors are marked 47 with a black stripe above. Took one out, measured, I get like 28pf. Maybe I heated it too much during desoldering.

So they must be 47pf caps but what does the black stripe stand for?

 

[ej25awd]

The black stripe/paint on the top signifies the ceramic capacitor's temperature coefficient, which is NP0/C0G. Look up capacitor temperature coefficient.

Your meter might not have the absolute accuracy to measure low value capacitance so don't blame the capacitor.

NP0/C0G are the best ceramic dielectric for audio. Their value is stable with temperature and DC bias and has very low dissipation factor. It will be a complete waste of time and money to replace them.

 

[DF96]

It could be worse than that: if poor soldering/desoldering is going on then the PCB could be damaged and the item may never work again. All because he wants to replace a good cap with a very slightly inferior cap!

Be aware that measuring small capacitances is prone to error, so check your equipment calibration and technique.

 

[lucpes]

I have a desoldering station but as I think of it 47pf is some kind of compensation way beyond the audio band. Thanks for the answers.

 

[Monte McGuire]

FWIW, NASA did some reliability tests with C0G multilayer ceramic caps, and they found that their reliability was not statistically affected even when used at 10x their rated voltage. So, for the C0G dielectric, the voltage rating is somewhat meaningless, as they can be used with equivalent reliability at 10x their rated voltages. While higher voltage parts may perform very slightly better, there is little risk of dielectric breakdown for any of these caps in low voltage circuits, regardless of faceplate voltage.